The most important objective in this research is to study the metabolism of NG-monomethyl-Larginine, an endogenously synthesized compound, and to identify one of the metabolites as N-methylurea, a compound which can be nitrosated to give rise to 1-N-methyl,1-N-nitrosourea, one of the most potent carcinogens known. This will be pursued with the following aims. (1) To study the metabolic pathways of NG-monomethyl-L-arginine. This involves hydrolytic cleavage, oxidative demethylation and decarboxylation. (2) To investigate the possible formation of N-methylurea from NG-monomethyl-L-arginine. (3) To further purify protein methylase I which methylates the guanidino group of protein-bound arginine residues. (4) To investigate the possible antitumor effects of NG-monomethyl-L-arginine on tumor cells in tissue or cell culture.